An exoplanet is a planet that is a distant star’s offspring and resides outside of our own Solar System. Some of those alien worlds resemble the planets that inhabit the family of our Sun, while others are so different that they are true “oddballs”—unlike anything that astronomers have observed in our Solar System. As the astronomers have come to the inevitable conclusion in the process of hunting for distant alien worlds beyond our Star that planets can be composed of almost anything. In December 2019, unlike anything ever seen before, a team of astronomers announced their discovery of a whole new class of planet. These “puffed up” oddballs are so bloated that they are nearly the same size as Jupiter, but its mass is only 1/100th.
Mercury Venus, Earth, and Mars are the planets that inhabit our own Solar System. In dramatic contrast, both are classified as gas giants by the most massive outer planet quartet, Jupiter and Saturn. Uranus and Neptune, the two outermost of the enormous planets, are different in composition from the gas giants and are classified as ice giants.
Like our own Earth, the quartet of earthly planets is solid worlds that are primarily composed of silicate rocks or metals. All four worlds bask inside our Solar System ‘s warm and well-lit inner zone and are comparatively close to our Planet. They are situated between our roiling Star and the Central Asteroid Belt which is between Mars and Jupiter.
The massive pair of gas giants, Jupiter and Saturn, are carbon-laden planets made mainly of hydrogen and helium. Gas giants are sometimes called ‘failed stars’ This is because they have the same essential elements as a star.
In the 1990s astronomers came to realize that Uranus and Neptune, unlike their two much larger gaseous siblings, are really a distinct class of planets. This pretty bluish duo is both classified as ice giants. Ice giants are composed mainly of heavier elements than hydrogen and helium — the two lightest atomic elements. These two distant worlds are made up of heavier atomic elements like oxygen, carbon, sulfur, nitrogen, etc.
Alien worlds called “Cotton candy” are currently known as Super Puffs. These puffy planets could represent a transitory, short-lived phase in planetary evolution. Because this phase is brief, it could explain why astronomers in our Solar System do not see anything like it. It was suggested that Super Puffs might have been born farther away from their stars, and then migrated inward to their stellar parents’ heat and warmth. At this stage, their low-density hydrogen and helium atmospheres migrate off into the vacuum between planets. Far smaller planets could be left behind in the future to tell their story.
Our Star’s Familiar Planets
As of 1 December 2019, there are 4,135 confirmed exoplanets inhabiting 3,073 worlds, and more than one single planet sporting 673. Some of these planets bear a close resemblance to those in our Star’s familiar family of major planets, while others are so exotic that astronomers never dreamed that such worlds could exist — until they were discovered.
Within our own Solar System, the three main planet groups are different from each other. The quartet of inner earth planets all displays a solid surface, making them look very different from the quartet of outer gaseous planets — both the two giants of gas and the two giants of ice. The four larger outer planets contain some hydrogen, helium, and water combinations that exist in a variety of physical states.
The terrestrial planets in our solar system possess the same fundamental form of structure. This means that all four small, rocky planets have a central metallic core, composed largely of iron with a silicate mantle around them. Earth’s Moon resembles the four main inner planets, but it has a much smaller mass of carbon.
There were probably many more earthly planets during the early years of our Solar System when it was first in the process of forming. However, most of these ancient terrestrial planetesimals are thought to have collided and merged with each other — or the four existing terrestrial planets have unceremoniously evicted from our solar system altogether.
The two heavily gas-blanketed banded behemoths, Jupiter and Saturn, are almost entirely made up of hydrogen and helium, with heavier atomic elements amounting to 3 to 13 percent of the mass. The two gas-giant denizens of the outer Solar system are thought to be made up of a translucent layer of molecular hydrogen covering a matrix of metallic hydrogen. It’s even believed the big pair would have molten rocky hearts.
The outermost region of their hydrogen atmosphere is composed of numerous layers of visible clouds that are primarily made up of water and ammonia. The metallic hydrogen coating accounts for the majority of both of the two stars, which is labeled “metallic” since the extremely high pressure allows hydrogen to turn into an electric conductor. It is assumed that the center of the giant pair consists of heavier components at such incredibly high temperatures that its properties are not well known.
The two outermost major planets are Uranus and Neptune, and they are composed mainly of elements heavier than hydrogen and helium. The word “storms” applies to volatile chemical substances with freezing points above around 100 K in astrophysics and planetary science, such as water, methane, or ammonia, with freezing points of 273 K, 91 K, and 195 K, respectively.
The constituent solids sported by the two ice giants were actually already solid, either directly in the shape of ices or frozen in water ice, when introduced into the pair during their creation. At the moment relatively little water exists in the form of ice in Uranus and Neptune. Instead, water mostly exists as a supercritical fluid at the temperatures and pressures within the duo.
The ice giants consist of only 20 percent mass about hydrogen and helium, in dramatic contrast to the gas-giants of our solar system, Jupiter and Saturn, both more than 90 percent massive hydrogen and helium.
The Strange Case Of The “Super Puff” Planets
The enigmatic super puff planets are often named “cotton candy planets,” because they feature the cotton candy scale. Recent observations obtained from NASA’s Hubble Space Telescope (HST) offered the first useful hints to a duet of such puffy worlds, all of which exist in the Kepler 51 network, chemistry. In addition, this particular exoplanet system comprises a trio of super puffs in orbit around a youthful star like the Earth. The device itself was discovered in 2012 by Kepler Space Telescope, a planet-hunting NASA. It wasn’t until 2014, however, that the extremely low density of these exotic worlds of “cotton candy” was determined — to the amazement of many planetary scientists.
The recent HST observations allowed a team of astronomers to more accurately determine the size and mass estimates for these planets — independently validating their “puffy” character, which is extremely low density. Though these strange “cotton candy” worlds are no more than multiple times the mass of our own planet, their hydrogen and helium atmospheres are so bloated that they are almost the size of the banded behemoth Jupiter of our own Solar System. Though the super puffs are nearly Jovian in scale, they are around a hundred times lighter in mass terms.
How and why the atmospheres expanded outward from these exotic super puffs are unknown. Yet their inflated atmospheres have made them particularly fascinating targets for further atmospheric studies. Using HST, the astronomers’ team went on the hunt for further clues. They were particularly interested in searching for water in planetary atmospheres, dubbed Kepler 51 b, and 51 d. HST observed the planets as they transited (passed by) their parent star’s glaring face. The scientists tried to detect the infrared hue of their sunsets — thus deciding the amount of energy that the environment receives in infrared light. This type of observation allows planetary scientists to search for the tattle-tale signs of the chemical components of the planet — like water.
The HST astronomers were shocked to note that no tattle-tale chemical signatures were observed on the spectra of both planets. This result was attributed by the scientists to clouds of particles floating high in their atmosphere. “This was totally unforeseen,” Dr. Jessica Libby-Roberts clarified in a December 2019 Hubble Observatory Press Release. “We had intended to detect broad water absorption features but they were just not there. Dr. Libby-Roberts is from Boulder University of Colorado.
Like the Earth’s own water clouds, the “cotton candy” planet clouds growing consist of salt crystals or photochemical hazes, close to those present on the largest satellite of Saturn, Titan. The surface of Titan is blanketed with a thick smog of golden-orange hydrocarbons.
The Kepler 51 b and 51 d clouds match up against other low-mass, gaseous planets outside our Solar System. When contrasting the “cotton candy” planets’ flat spectra against the spectra of other worlds, the astronomers were able to formulate a theory that cloud and haze forming are related to a planet’s temperature—the hotter a planet becomes, the more cloudy it is.
The astronomers were also investigating the possibility that these planets might not really be super puffs. The gravitational force between planets allows the creation of small shifts in their orbital times. These timing effects help to decide planetary masses. By combining the timing variations of when a planet floats in front of its parent star’s fiery face (transiting) with those transits observed by the Kepler Space Telescope, scientists were better able to constrain the system’s planetary masses and dynamics. Their results for Kepler 51 b proved to be in agreement with previous measured ones. However, they noticed that Kepler 51 d was somewhat less massive (or the earth was much puffier) than previously calculated.
Finally, the team concluded that these planets’ low densities are partly the result of the system’s young age, which is just 500 million years old. By comparison, 4.6 billion years ago our very own Sun was born. Models suggest that such “cotton candy” planets evolved outside of what is called a star’s snow sheet. The snow line for a star is a region of potential orbits where icy materials can survive. Ultimately, the planets of this youthful system migrated inward towards their stellar parent, in a manner that was compared to a “railway car string.”
With the planets much closer to their star now, their low-density atmospheres are expected to evaporate into space in the next few billion years. Using planetary evolution models, the astronomers’ team demonstrated that Kepler 51b—the planet closest to its star—will look much like a smaller and hotter version of Neptune from our own Solar System in a billion years or so. This particular type of exoplanet is quite common throughout our Galaxy on the Milky Way.
It seems, though, that Kepler 51 d, which is further from its parent-star, will tend to be a low-density oddball world — though it will also diminish and lose a slight amount of its puffy atmosphere. “This device offers a rare platform for evaluating early earth evolution hypotheses,” Dr. Zach Berta-Thompson commented in the Hubble Observatory Press Release in December 2019. Dr. Berta-Thompson is also from Boulder University of Colorado.
Astronomers will eventually be able to assess the chemical structure of the puffy world pair with the forthcoming NASA’s James Webb Space Telescope (JWST). JWST will have a sensitivity to longer infrared wavelengths of light and may pierce through the layers of the cloud. Future observations with this telescope could shed new light on the actual composition of these puffy oddballs, thus solving an intriguing mystery.